The present invention relates to trays on which magnetic heads for hard-disk drives are mounted and subjected to processing, cleaning, transfer, storage, etc. More particularly, the invention relates to trays for carrying magnetic heads for magnetic disks and are suitable for the transfer of magnetoresistive heads (MR heads).
Trays for magnetic heads have conventionally been produced by molding a conductive thermoplastic resin composition obtained by incorporating and dispersing a conductivity-imparting ingredient, e.g., an antistatic agent or carbon black, into an ABS resin or the like.
However, the incorporation of an antistatic agent has the following and other drawbacks: electrical conduction is influenced by the ambient humidity because the mechanism of electrical conduction is attributable to ionic conduction; the antistatic agent flows out upon cleaning and during long-term use, resulting in reduced antistatic properties; and addition of a large amount of an antistatic agent impairs heat resistance. The incorporation of carbon black has the following drawback. Although carbon black is uninfluenced by humidity, cleaning, etc., it should be added in a large amount for imparting conductivity. As a result, the surfaces of moldings have poor resistance to scratching and wearing and are hence apt to release wearing dust and carbon particles (i.e., particles).
For eliminating these problems, a material obtained by adding carbon fibers to, for example, a polycarbonate is used as trays for magnetic heads for hard disks. Compared to carbon black, carbon fibers are more effective in diminishing particle detachment.
In general, a magnetic head comprises an arm part, a head chip attached to the tip of the arm part, and a lead wire connected to the head chip. An MR head employs an MR element (magnetoresistive element) as the head chip.
MR (magnetoresistive) heads are recently coming to be mainly used in place of conventional thin-film heads in order to heighten the density of heads. In this trend, however, even a material containing carbon fibers has come not to fully satisfy a property requirement.
Namely, although trays made of a material containing carbon fibers as a conductive loading material are reduced in particle detachment as compared with trays made of a material loaded with carbon black, trays for MR heads have come to be required to attain a further diminution of particle detachment.
This is because not only MR heads themselves are sensitive to conductive particles, but also disk crushing caused by particles has come to occur frequently in practical use of MR heads due to the head/magnetic disk clearance which has become exceedingly small.
That is, particle generation from a tray for magnetic heads for hard disks occurs when fibers themselves detach from the tray surface or a resin ingredient peels off fibers, for example, in a step in which heads are cleaned with pure water with application of ultrasonic. Such particle detachment not only fouls and damages heads, but also has a fear that during use of the hard-disk drive, the particles present between the head and the hard disk serve as a foreign matter to cause head crushing.
Incidentally, the conventional thin-film head detects signals based on the current which generates when a signal magnetic field approaches the coil. In contrast, in the MR head, a slight sensing current is caused to flow through the MR element and a signal magnetic field is detected based on current resistance. Consequently, there is a high possibility in the MR head that even a slight noise current might damage the MR element. Because of this, as compared with conventional integrated magnetic heads and ICs, the MR head is far more sensitive to an electrostatic discharge attributable to a potential difference between the magnetic head and a tray and to a contact current generating upon head/tray contact.
Namely, in a process for assembling an MR head, a lead wire is connected to a head chip and an arm part is attached to a gimbal through the head chip. Although this lead wire (metal wire) is coated with a polyimide, the polyimide/metal wire contact area is always in a charge-separated, electrically unstable state due to the contact potential difference between the polyimide and the metal wire. As a result, a contact of the lead wire tip to a magnetic-head tray or the like is more apt to result in charge transfer in the contact area and this increases the possibility of damage.
Conventional trays for magnetic heads have a surface resistance of about from 101 to 102 xcexa9/xe2x96xa1. Although such trays have no possibility of head damage caused by electrostatic discharge, they pose a serious problem that damage is caused by an excessive contact current which flows between a head and the tray or between a peripheral part and the tray due to the too low surface resistance of the tray.
In addition, a material containing carbon fibers as a conductive loading material is apt to give trays having a considerably low surface resistance. Reducing the addition amount of carbon fibers for heightening the surface resistance results in unstable contact among carbon fibers within the tray, making it impossible to obtain evenness of resistivity.
Trays made of a material containing carbon fibers further have the following problem. During cleaning with pure water, chlorine ions contained as an impurity in the carbon fibers dissolve away in the pure water. The released chlorine ions may corrode the magnetic head or serve as a foreign matter in the space between the head and a disk.
Magnetic heads are mounted on a tray so as to be in direct contact therewith, and are subjected to assembly, cleaning, transfer, and discharge. In this process, the magnetic heads are taken out of and replaced on the tray many times and, hence, friction is produced by contacts between the tray surface and the magnetic heads.
On the other hand, conventional trays for carrying magnetic heads are made of a material obtained by incorporating carbon fibers for imparting conductivity into a polycarbonate. The surfaces of magnetic-head carrying trays constituted of such a conductive polycarbonate resin composition have carbon fibers exposed thereon. Because of this and because of minute uneven surface flows during molding, these surfaces are extremely rough.
This surface roughness has aroused a problem that the polyimide coating film and the lead wire of a magnetic head suffer damage when the tray comes into contact or friction with the magnetic head.
In contrast to the conventional thin-film head in which signals are detected based on the current which generates when a signal magnetic field approaches the coil, this MR head is a device in which a slight sensing current is caused to flow through the MR element and a signal magnetic field is detected based on current resistance. Due to this mechanism, the MR head has greatly improved detection sensitivity and this enables a reduced track pitch and hence an increased capacity in media. Recently, a GMR head has come to be used which is intended to attain a further increase in capacity.
The MR head and the GMR head are extremely sensitive to contamination with, e.g., a slight amount of a corrosive gas and a slight noise current. Because of this, not only trays for carrying these heads but also various handling parts and jigs have come to be required to satisfy server performance requirements for avoiding head fouling.
The conventional trays for carrying magnetic heads include trays produced by molding a resin composition obtained by incorporating carbon fibers into a polycarbonate resin.
The polycarbonate resin used here is usually one produced by a solution method in which an alkaline aqueous solution of a dihydric phenol is reacted with phosgene in the presence of an organic solvent. By this method, a polycarbonate resin is obtained as a solution thereof in the organic solvent. As this organic solvent, chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride and chlorinated aromatic hydrocarbons such as chlorobenzene and chlorotoluene are used. The most generally used one is methylene chloride.
The polycarbonate resin is obtained by removing the solvent phase from the resultant polycarbonate resin solution by vaporization to conduct separation and purification. In this case, however, the organic solvent represented by methylene chloride remains in the resin although in a slight amount, because it has an excellent affinity for polycarbonates. After the resin is molded into magnetic-head carrying trays as a final product, the methylene chloride remaining in the resin generates as a volatile ingredient during the use of the trays.
The substances which have been thought to be corrosive volatile ingredients in the conventional trays for carrying magnetic heads are mostly ionic substances such as hydrochloric acid and chlorine ions. However, in trays for carrying magnetic heads having an element extremely susceptible to corrosion, such as an MR element or GMR element, even a chlorine ion precursor such as methylene chloride has come to arouse a problem.
With respect to other volatile ingredients such as alcohols and ketones also, the safety thereof for magnetic head chips has not been fully ascertained. Because of this, trays for carrying magnetic heads have come to be required to be reduced also in total outgas amount.
The invention has been achieved in view of the above-described circumstances of conventional techniques. An object of the invention is to provide a tray for carrying magnetic heads for magnetic disks which has eliminated at least one of the problems described above.
The tray for carrying magnetic heads for magnetic disks according to the first aspect of the invention is a tray for carrying a magnetic head for magnetic disks which comprises an arm part, a head chip attached to the tip of the arm part, and a lead wire connected to the head chip, wherein the tray is one obtained by molding a conductive thermoplastic resin composition, and when the tray is immersed in 500 ml of pure water while applying 40 kHz ultrasonic thereto for 60 seconds, the number of particles having a particle diameter of 1 xcexcm or larger which detach from the surface of the tray is 5,000 pcs or smaller per unit surface area, cm2, of the tray.
Furthermore, when this tray has a surface resistance of from 103 to 1012 xcexa9, not only sufficient antistatic properties can be obtained but also an excessive contact current can be prevented from flowing upon contact with the tray. Consequently, magnetic heads can be prevented from suffering electrical damage.
This tray has such excellent surface evenness and stability that when the tray is immersed in 500 ml of pure water while applying 40 kHz ultrasonic thereto for 60 seconds, the number of particles having a particle diameter of 1 xcexcm or larger which detach from the surface of the tray (hereinafter, this value is referred to as xe2x80x9camount of particle generationxe2x80x9d) is 5,000 pcs/cm2 or smaller. Because of this, magnetic heads can be prevented from being physically or chemically fouled or damaged by the particles which have detached upon scratching, wearing, or cleaning.
The conductive thermoplastic resin composition is preferably one obtained by incorporating into a thermoplastic resin one or more conductive loading materials selected from the group consisting of polyether type polymeric antistatic agents, conductive fillers, and carbon fibrils. As the thermoplastic resin can be used one or more members selected from the group consisting of polycarbonates, poly(butylene terephthalate), poly(ethylene terephthalate), and polypropylene.
The tray for carrying magnetic heads for magnetic disks according to the second aspect of the invention is one obtained by injection-molding a conductive polycarbonate resin composition and having a surface roughness which satisfies the following (1) or (2) in a measurement employing a cutoff wavelength of 2.5 mm:
(1) the ten-point average roughness (Rz) is 5 xcexcm or smaller;
(2) the proportion of 10%-cutting-level load length (tp) is 1% or higher and the count of peaks not smaller than xc2x10.1 xcexcm based on the center line (Pc) is (0 or larger and) 100 or smaller per cm of the length of measurement.
This tray, which has a surface roughness satisfying (1) or (2) given above, can prevent magnetic heads from being damaged when the tray comes into contact or friction with the magnetic heads.
The tray for carrying magnetic heads for magnetic disks according to the third aspect of the invention is a tray for carrying a magnetic head for magnetic disks which comprises an arm part, a head chip attached to the tip of the arm part, and a lead wire connected to the head chip, wherein the tray is preferably one obtained by molding a polycarbonate resin composition containing a conductive loading material in an amount of from 0.25 to 50% by weight, and the amount of a chlorinated hydrocarbon generated from the tray having a surface area of 12.6 cm2 under the conditions of a heating temperature of 85xc2x0 C. and an equilibrium time of 16 hours is preferably 0.1 xcexcg/g or a smaller when determined with a head space gas chromatogram.
In this tray, the amount of a chlorinated hydrocarbon a generated from the tray having a surface area of 12.6 cm2 under the conditions of a heating temperature of 85xc2x0 C. and an equilibrium time of 16 hours (hereinafter referred to simply as xe2x80x9camount of chlorinated-hydrocarbon generationxe2x80x9d) is 0.1 xcexcg/g or smaller when determined with a head space gas chromatogram. Since this tray is thus reduced in the generation of volatile ingredients, the problem of magnetic-head corrosion damage can be eliminated.
The tray for carrying magnetic heads for magnetic disks according to the fourth aspect of the invention is a tray for carrying a magnetic head for magnetic disks which comprises an arm part, a head chip attached to the tip of the arm part, and a lead wire connected to the head chip, characterized in that the tray is one obtained by molding a conductive thermoplastic resin composition and having a surface resistance of from 1xc3x97105 to 1xc3x971012 xcexa9, and when the tray is immersed in 500 ml of pure water while applying 40 kHz ultrasonic thereto for 60 seconds, the number of particles having a particle diameter of 1 xcexcm or larger which detach from the surface of the tray is 3,500 pcs/cm2 or smaller. This tray can eliminate the problem of causing damage.
The tray for carrying magnetic heads for magnetic disks according to the fifth aspect of the invention is a tray for carrying a magnetic head for magnetic disks which comprises an arm part, a head chip attached to the tip of the arm part, and a lead wire connected to the head chip, characterized in that: the tray is one obtained by molding a conductive thermoplastic resin composition and having a surface resistance of from 1xc3x97103 to 1xc3x971012 xcexa9; when the tray is immersed in 500 ml of pure water while applying 40 kHz ultrasonic thereto for 60 seconds, the number of particles having a particle diameter of 1 xcexcm or larger which detach from the surface of the tray is 5,000 pcs/cm2 or smaller; the tray has such a surface roughness that the ten-point average roughness (Rz) thereof as determined through a measurement employing a cutoff wavelength of 2.5 mm is 5 xcexcm or smaller; and the amount of a chlorinated hydrocarbon generated from the tray having a surface area of 12.6 cm2 under the conditions of a heating temperature of 85xc2x0 C. and an equilibrium time of 16 hours is 0.1 xcexcg/g or smaller when determined with a head space gas chromatogram. This tray can eliminate damage occurrence.
The tray for carrying magnetic heads for magnetic disks according to the sixth aspect of the invention is a tray for carrying a magnetic head for magnetic disks which comprises an arm part, a head chip attached to the tip of the arm part, and a lead wire connected to the head chip, wherein the tray is one obtained by molding a conductive thermoplastic resin composition and having a surface resistance of from 1xc3x97103 to 1xc3x971012 xcexa9, and has such a surface roughness that in a measurement employing a cutoff wavelength of 2.5 mm, the proportion of 10%-cutting-level load length (tp) is lower than 4%. This tray can eliminate damage occurrence.